一：如图，首先布局计算器主页显示：

activity_main.xml

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent" >

android:id="@+id/num1"

android:layout_width="80dp"

android:layout_height="wrap_content"

android:inputType="number" />

android:id="@+id/type"

android:layout_width="40dp"

android:layout_height="50dp"

android:layout_toRightOf="@id/num1"

android:gravity="center" />

android:id="@+id/num2"

android:layout_width="80dp"

android:layout_height="wrap_content"

android:layout_toRightOf="@id/num1"

android:layout_marginLeft="50dp"

android:inputType="number" />

android:id="@+id/equal"

android:layout_width="80dp"

android:layout_height="50dp"

android:layout_toRightOf="@id/num2"

android:gravity="center" />

android:id="@+id/add"

android:layout_width="70dp"

android:layout_height="wrap_content"

android:layout_below="@id/num1"

android:text="@string/add" />

android:id="@+id/sub"

android:layout_width="70dp"

android:layout_height="wrap_content"

android:layout_toRightOf="@id/add"

android:layout_alignTop="@id/add"

android:text="@string/sub" />

android:id="@+id/mul"

android:layout_width="70dp"

android:layout_height="wrap_content"

android:layout_toRightOf="@id/sub"

android:layout_alignTop="@id/sub"

android:text="@string/mul" />

android:id="@+id/div"

android:layout_width="70dp"

android:layout_height="wrap_content"

android:layout_toRightOf="@id/mul"

android:layout_alignTop="@id/mul"

android:text="@string/div" />

二 计算器实现的方法：

public class CalculatorBiz {

public float add(float num1,float num2){

return num1+num2;

}

public float sub(float num1,float num2){

return num1-num2;

}

public float mul(float num1,float num2){

return num1*num2;

}

public float div(float num1,float num2){

return num1/num2;

}

}

三 MainActivity主要方法：

public class MainActivity extends Activity {

//定义组件

private EditText inputnum1;

private EditText inputnum2;

private TextView type;

private TextView equal;

private Button add;

private Button sub;

private Button mul;

private Button div;

CalculatorBiz calculator=new CalculatorBiz();

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

//查找组件

inputnum1=(EditText) findViewById(R.id.num1);

inputnum2=(EditText) findViewById(R.id.num2);

type=(TextView) findViewById(R.id.type);

equal=(TextView) findViewById(R.id.equal);

add=(Button) findViewById(R.id.add);

sub=(Button) findViewById(R.id.sub);

mul=(Button) findViewById(R.id.mul);

div=(Button) findViewById(R.id.div);

type.setTextColor(Color.WHITE);

equal.setTextColor(Color.WHITE);

add.setOnClickListener(new OnClickListener() {

@Override

public void onClick(View v) {

String num1=inputnum1.getText().toString();

String num2=inputnum2.getText().toString();

float a=Float.parseFloat(num1);

float b=Float.parseFloat(num2);

type.setText("+");

equal.setText("="+calculator.add(a, b));

}});

sub.setOnClickListener(new OnClickListener() {

@Override

public void onClick(View v) {

String num1=inputnum1.getText().toString();

String num2=inputnum2.getText().toString();

float a=Float.parseFloat(num1);

float b=Float.parseFloat(num2);

type.setText("-");

equal.setText("="+calculator.sub(a, b));

}});

mul.setOnClickListener(new OnClickListener() {

@Override

public void onClick(View v) {

String num1=inputnum1.getText().toString();

String num2=inputnum2.getText().toString();

float a=Float.parseFloat(num1);

float b=Float.parseFloat(num2);

type.setText("*");

equal.setText("="+calculator.mul(a, b));

}});

div.setOnClickListener(new OnClickListener() {

@Override

public void onClick(View v) {

String num1=inputnum1.getText().toString();

String num2=inputnum2.getText().toString();

float a=Float.parseFloat(num1);

float b=Float.parseFloat(num2);

type.setText("/");

equal.setText("="+calculator.div(a, b));

}});

}

@Override

public boolean onCreateOptionsMenu(Menu menu) {

super.onCreateOptionsMenu(menu);

menu.add(0, 1, 0, "关于");

menu.add(0, 2, 1, "退出");

menu.findItem(2);

return true;

}

public boolean onOptionsItemSelected(MenuItem item){

if(item.getItemId() == 1){

Toast.makeText(this, "详细内容\n"+"作者：dyp\n"+"版本：version1", Toast.LENGTH_LONG).show();

}else if(item.getItemId() == 2){

Toast.makeText(this, "退出\n"+"你确定退出程序？", Toast.LENGTH_LONG).show();

}

return super.onOptionsItemSelected(item);

}

}